1. Technical Field of the Invention
The invention relates generally to communication systems; and, more particularly, it relates to generation of coding that may be employed to generate coded signals for use in such communication systems.
2. Description of the Related Art
Data communication systems have been under continual development for many years. One such type of communication system that has been of significant interest lately is a communication system that employs iterative error correction codes. Of particular interest is a communication system that employs LDPC (Low Density Parity Check) code. Communications systems with iterative codes are often able to achieve lower bit error rates (BER) than alternative codes for a given signal to noise ratio (SNR).
A continual and primary directive in this area of development has been to try continually to lower the SNR required to achieve a given BER within a communication system. The ideal goal has been to try to reach Shannon's limit in a communication channel. Shannon's limit may be viewed as being the maximum possible data rate to be used in a communication channel, having a particular SNR (Signal to Noise Ratio), that achieves error free transmission through the communication channel. In other words, the Shannon limit is the theoretical bound for channel capacity for a given modulation and code rate.
LDPC code has been shown to provide for excellent decoding performance that can approach the Shannon limit in some cases. For example, some LDPC decoders have been shown to come within 0.3 dB (decibels) from the theoretical Shannon limit. While this example was achieved using an irregular LDPC code of a length of one million, it nevertheless demonstrates the very promising application of LDPC codes within communication systems.
The use of LDPC coded signals continues to be explored within many newer application areas. For example, the use of LDPC coded signals has been of significant concern within the IEEE (Institute of Electrical & Electronics Engineers) P802.3an (10GBASE-T) Task Force. This IEEE P802.3an (10GBASE-T) Task Force has been created by the IEEE to develop and standardize a copper 10 Giga-bit Ethernet standard that operates over twisted pair cabling according the IEEE 802.3 CSMA/CD Ethernet protocols. Carrier Sense Multiple Access/Collision Detect (CSMA/CD) is the protocol for carrier transmission access in Ethernet networks. IEEE 802.3an (10GBASE-T) is an emerging standard for 10 Gbps (Giga-bits per second) Ethernet operation over 4 wire twisted pair cables. More public information is available concerning the IEEE P802.3an (10GBASE-T) Task Force at the following Internet address:
“http://www.ieee802.org/3/an/”.
This high data rate provided in such applications is relatively close to the theoretical maximum rate possible over the worst case 100 meter cable. Near-capacity achieving error correction codes are required to enable 10 Gbps operation. The latency constraints, which would be involved by using traditional concatenated codes, simply preclude their use in such applications.
Clearly, there is a need in the art for some alternative coding types and modulation implementations that can provide near-capacity achieving error correction. LDPC codes offer such performance.
There is no generally agreed “best” method to follow for the construction of LDPC codes with good performance. In the following reference, an LDPC code is constructed based on two codewords of an R-S (Reed-Solomon) code.
[a] I. Djurdjevic, J. Xu., K. Abdel-Ghaffar, and S. Lin, “A Class of Low-Density Parity-Check Codes Constructed Based on Reed-Solomon Codes with Two Information Symbols,” IEEE Communications Letters, Vol. 7, No. 7, July 2003, pp. 317-319.
However, the LDPC codes presented using the approach of this prior art reference are of a very narrow type and there is very little, if any, flexibility presented by this approach by which other types of LDPC codes may be designed. This lack of flexibility presents a significant challenge for any design of such LDPC codes and/or communication devices to be implemented using such LDPC codes. Clearly, there seems to be a continual need for additional and better types of codes for use in various communication systems to provide for better means of error correction and better BER (Bit Error Rate) while operating at various amounts of SNR (Signal to Noise Ratio).